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Discussion Starter · #1 · (Edited)
I have a 2008 GTI (APR Stage I, 94000 miles) with all stock hardware under the hood. After my car is sitting in the driveway over night, starting my car causes it to make a frightening knocking noise that lasts for five seconds before stuttering and then finally calming down. If my car sits for a short amount of time before starting it, ignition feels correct. So I conclude something is happening as time passes and the car sits unused. The CEL blinks for the entire duration of the knocking before becoming solid. Acceleration is normal. Notwithstanding, I can feel the misfires when cruising.

A scan revealed random misfires at 3 & 4. In response, I replaced the 3 & 4 injectors. The problem continued, so I decided to swap coils with 1 & 3 and spark plugs with 2 & 4. The issue remained. An additional scan showed random misfires at 3 & 4. I reason the plugs and coils are fine, unless otherwise suggested.

I have done extensive research on MYFASTGTI.com, showing other variables that may be responsible for my problem:

  • Clogged Intake Runners
  • Cam Position Sensor
  • Throttle Body

If I am missing another possible culprit, please let me know. Of the three, which is the easiest to check? How should I prioritize my approach? Which has the highest probability of being responsible for my problem?

If additional information is needed, please let me know. Thanks in advance!

EDIT: I have additional information. I had my brother stand behind the car before I started it, after the car sat for 12+ hours. When the misfiring was heavy, black smoke came out of the exhaust, indicating rich misfires.
 

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You need to clean the intake valves.
You can try a quick blow-by method
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Discussion Starter · #3 ·
Thank you for the prompt response ROH ECHT. I will clean the intake valves and observe the results. Meanwhile, any other suggestions from anyone and everyone will certainly be accepted.
 

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Discussion Starter · #4 ·
You need to clean the intake valves.
You can try a quick blow-by method
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Cleaned the intake valves by removing the manifold and scraping them. I will post another update in a couple days of driving to provide an accurate result.
 

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Discussion Starter · #5 ·
You need to clean the intake valves.
You can try a quick blow-by method
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It has been a couple days and it seems ROH ECHT was correct. The intake valves had, what appeared to be, a significant amount of material on them. By removing the material, the vehicle is behaving. Cold starts are no longer a problem. Thank you!
 

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You bet.
 
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